The lumen of blood vessels is lined by endothelial cells (ECs). The latter lie on a basement membrane whose structural elements include laminins, proteoglycans and collagens. ECs interact with these matrix proteins, in part, via receptors called integrins. Such interactions are involved in regulating a number of cellular functions including adhesion, motility and gene expression. In the adult, endothelial cells in the vessels are quiescent. However, in wound healing and in pathological conditions including cancer and inflammatory diseases, a stimulus activates new vessel growth, a process called angiogenesis. In this application, our studies are focused on a novel matrix junction that we recently identified in ECs. Preliminary experiments indicate that endothelial cells assemble a novel focal contact-like structure that is associated with both the microfilament and vimentin cytoskeletons. This vimentin-associated matrix adhesion (VMA) possesses, at its core, the avbeta3 integrin heterodimer and an a4 laminin subunit-containing ligand in the extracellular matrix. In addition, the VMA characteristically contains plectin that we hypothesize is involved in mediating cell surface anchorage of the vimentin cytoskeleton. This junction assembles in a growth factor-dependent manner and appears to play a role in EC migration and branching morphogenesis, essential elements of angiogenesis, since antibodies against both the avbeta3 integrin heterodimer and the a4 laminin subunit inhibit these events. In aim 1, we will undertake further characterization of the molecular composition of the VMA with particular emphasis on how its protein components interact and on identification of the molecules involved in anchorage of the vimentin cytoskeleton at the cell surface. In aim 2, we will study the dynamics of assembly of the VMA in living ECs in which we have expressed VMA proteins tagged with green fluorescent protein. In aim 3, we will analyze the function(s) of components of the VMA in angiogenesis in vivo. These studies will provide new insight into the role of integrin/matrix interactions in angiogenesis.